The separate enantiomers of some chiral drugs have different therapeutic properties, and/or mechanisms of action and yet in some cases it may still be desirable to dose both enantiomers together. However, where the pharmacokinetic properties of the separate enantiomers are different, for instance due to differences in the rates at which they are metabolised, the ratio of the different enantiomers changes with time after initial dosing, which can lead to reduced efficacy of the drug. The actual enantiomeric ratio at any one time may be dependent upon a number of factors, and may be further complicated if different dosage forms provide different enantiomeric ratios. Effects such as these have been observed with the different enantiomers of Verapamil, for instance see Longstreth, J. A. Clin. Pharmacol. (1993) 18 (2nd Edition): 315-336 and Gupta et al., Eur. J. Pharm. Biopharm. (1996) 42(1): 74-81.